While there’s no shortage of ink and pixels being spilled over the fact that Yahoo’s (YHOO) new CEO Marissa Mayer is the first pregnant head of a Fortune 500 company, the only Mayer delivery that should matter to investors is improved performance for Yahoo’s stock.

And all the chatter aside, based on revenue, Mayer is way down the list of female CEOs. There are currently 19 female CEO’s running Fortune 500 companies -- yep, a paltry 3.8% -- and Mayer’s Yahoo is the second to last on that list, and #483 in the overall rankings. And though hints to Mayer’s approach at Yahoo are starting to emerge, it’s early to suggest whether she can turn the company around or not.

Meg Whitman, CEO of Hewlett Packard (HPQ) is the highest ranking female CEO on the Fortune 500 list at #10. Whitman, who stepped into the CEO office last September handily beats Mayer as chief of Silicon Valley’s biggest basket case.

Given that Rometty just took over this past January at IBM, it’s too early to measure her impact on the company’s bottom line. Let’s just say Yahoo’s Mayer would surely love to be inheriting IBM’s trend lines:

Kraft has outperformed the broad market since Rosenfeld took over in mid 2006. The next challenge is how the market responds to the planned 2012 split of the company into two public companies: one focusing on snack brands—which Rosenfeld will continue to run-and the other covering the food giant’s North American grocery business.